Summary A psychosomatic study was made of consecutive patients with all types of leukemia and lymphoma as they were admitted to a general hospital. Reported here are the first 20 men and boys studied. In all of these cases, the symptoms and the recognition of the disease occurred while the patient was having to adjust to multiple stresses, which arose from multiple sources. In 17 of the 20 patients, these stresses included separation from a significant person, father, mother, wife, or other mother-figure, usually by death. Such separation also occurred with advent of sibling rivals as actual siblings or offspring. Frequently there were coincidental problems in life adjustment related to work, infection, injury, or operation. The symptoms leading up to the recognition of lymphoma or leukemia, and manifested during the course of the diagnosed illness, frequently included anorexia, nausea, vomiting, pain, and varying degrees of anxiety reaction and depression. After recognition of the lymphoma or leukemia, these symptoms frequently could not be correlated with the extent or degree of activity of the lymphomatous pathology, and could be understood on a psychological basis. Suggestion is made that the various symptoms and the reaction observed in the reticuloendothelial system may have been responses to the psychological stresses. The reticuloendothelial tissue is discussed as a mechanism for dealing with derangement of equilibrium within the organism. Three hypotheses are suggested. One involves consideration of the reticuloendothelial system in terms of anxiety or the fight-flight responses, and second, consideration in terms of a mechanism to deal with noxious agents, including psychic stress, within the organism. The third possibility considered is that alteration in the reticuloendothelial system may occur as a nonspecific response to changes in the organism more specifically related to psychological stress. This study suggests that pathological activity of the reticuloendothelial system may occur as part of a reaction to psychological stresses. It is indicated also that further psychosomatic study of patients with leukemia and lymphoma may help to clarify the nature of these disorders.